What is the role of lab tests in the workup of mastocytosis?

Updated: Sep 16, 2020
  • Author: Jacquiline Habashy, DO, MSc; Chief Editor: Dirk M Elston, MD  more...
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Consider the following laboratory tests:

  • CBC count: In systemic mastocytosis, CBC counts may reveal anemia, thrombocytopenia, thrombocytosis, leukocytosis, and eosinophilia.

  • Plasma or urinary histamine level: Patients with extensive cutaneous lesions may have 24-hour urine histamine excretion at 2-3 times the normal level.

  • Total tryptase level: Tryptase is a marker of mast cell degranulation released in parallel with histamine. Total tryptase levels in plasma correlate with the density of mast cells in urticaria pigmentosa lesions in adults with systemic mastocytosis. Patients with only cutaneous mastocytosis typically have normal levels of total tryptase. Total tryptase values are recommended by the WHO as a minor criterion for use in the diagnostic evaluation of systemic mastocytosis. [1, 2, 37] The total tryptase level in serum or plasma seems to be a more discriminating biomarker than urinary methylhistamine for the diagnosis of systemic mastocytosis. [37] Most patients with systemic anaphylaxis of sufficient severity to result in hypotension have elevated serum or plasma beta-tryptase levels. During insect sting–induced anaphylactic hypotension, beta-tryptase levels in the circulation are maximal 15-120 minutes after the sting. [37]

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